Polypropylene, especially highly isotactic polypropylene, has been used in many applications in the form of molded articles, film, sheet, etc., because it is excellent in molding processability, toughness, moisture resistance, gasoline resistance, chemical resistance, has a low specific gravity, and is inexpensive. The use of polypropylene polymers is expanding at an increasing rate in the fields of exterior and interior automotive trims, in electrical and electrical equipment device housing and covers as well as other household and personal articles.
However, polypropylene is poor or inadequate in heat resistance, stiffness, scratch resistance and impact resistance. These deficiencies are obstacles to opening up new applications for polypropylene, particularly applications which have traditionally been injection molded. In order to overcome these shortcomings, especially inadequate impact resistance, polypropylene has been blended with a rubbery elastic material such as ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber or ethylene-butene copolymer rubber. For examples, see U.S. Pat. No. 5,391,618 which discloses low crystalline polypropylene polymer compositions comprising an ethylene alpha-olefin copolymer, U.S. Pat. No. 5,576,374 which discloses polypropylene polymer compositions comprising a substantially linear ethylene polymer and U.S. Pat. No. 5,639,829 which discloses propylene polymer compositions comprising an ethylene and 1-buttene random copolymer. However, while impact properties are improved these propylene polymer compositions do not achieve a good balance of stiffness and toughness.
In view of the deficiencies of the conventional propylene polymers and blends thereof, it would be highly desirable to provide a propylene polymer composition which exhibits improved processability with a good balance of stiffness and toughness which demonstrates improved scratch resistance in injection molded articles.